This invention relates to a control device for internal combustion engines having a supercharger system and an adjustable intake valve system.
Such a control device is known from German patent document DE 43 12 085 A1, for example. This known control device is concerned with adjusting an optimum valve overlap as a function of load and rotational speed of the internal combustion engine specifically in supercharged internal combustion engines. Only the control time for opening is taken into account, but the control time for closing the intake valve is not. The control device described here addresses the problem that in the case of valve overlap, unburned fuel can be blown through the cylinder by the supercharger system, the so-called blow-by effect.
Other known control devices devoted to the adjustment of optimum valve overlap disregard the problem that in the lower partial load range, residual gases may flow into the cylinder due to the negative flushing gradient, these gases initially contributing to dethrottling of the charge cycle but above a certain level they are capable of preventing stable combustion.
The object of the invention is to improve upon a control device of the type defined in the introduction, so that fuel consumption is reduced, at least in the partial load range, while excessive valve overlap is prevented.
According to this invention, fuel consumption is reduced especially in the partial load range by dethrottling with early intake closure while at the same time preventing excessive valve overlap without any change in the total intake control time. The subject matter of the invention is the application of a fixed reduced intake control time with a supercharger system. According to this invention, preferably a system having an exhaust turbocharger or compressor supercharger is used as the supercharger system.
With the inventive control device for internal combustion engines having a supercharger system and a system for adjusting the control times of at least one intake valve of a cylinder within a predetermined adjustment range, starting from a zero position up to a maximum adjustment position, adjusting it by a defined maximum possible crank angle range in the direction of advanced ignition, the intake length of the intake cam assigned to the intake valve is designed so that the control time for closing the intake valve is at or before the crank angle (° CA) assigned to bottom dead center (BDC) of the charge cycle of the cylinder piston when the zero position prevails with the system for adjusting the control times. Systems for adjusting the control times by rotation of the camshaft in particular have also long been known by the abbreviation VANOS.
The zero position here corresponds to the greatest intake spread, i.e., the maximum adjustment position in the direction of delayed ignition. The intake length is usually defined in relation to a predetermined opening and closing valve lift of somewhat more than 0 mm, here preferably 1 mm opening and closing lift, so the asymptotic starting and ending curves of a valve lift diagram are “truncated” with regard to a sharper curve.
The intake length of the intake cam assigned to the intake valve is preferably designed so that the control time for closing the intake valve occurs before the crank angle assigned to bottom dead center of the charge cycle of the cylinder piston when the maximum adjustment position occurs in the system for adjusting the control times by the total adjustment range in the direction of advanced ignition.
In addition, the intake length of the intake cam assigned to the intake valve is additionally designed so that at a maximum possible adjustment of the control times in the direction of advanced ignition for dethrottling of the charge cycle procedure due to early intake closing time, a predetermined maximum allowed valve overlap is not exceeded.
On the whole, the inventive intake length, i.e., the effective intake control time (beyond an opening and closing height of the intake valve of approximately 1 mm) of the intake cam assigned to the intake valve is preferably between a crank angle of approximately 150° and a crank angle of approximately 190°.
The invention is based on the finding that the intake volume is limited by shifting the intake closing in the direction of advanced ignition, preferably by the amount of the full VANOS adjustment range, which is known to be CA 60° to CA 70°, for example, with regard to bottom dead center in the intake cycle during the charge cycle. This yields fuel savings. The inventive approach here involves only using a “shorter” cam (intake length above 1 mm valve lift <190° crank angle (° CA)) in comparison with the cams generally used (intake length above 1 mm valve lift >200°). This is possible because the disadvantage of the short intake camshaft control time with regard an adequate volume of fresh air for combustion can be compensated because of the increased supercharging pressure of the supercharger system. For this invention, no complex additional systems for adjusting the control times, such as systems for camshaft shifting (e.g., VVT) or fully variable valve controls (e.g., EVT), are required.
The invention is also based on the finding that merely shifting the intake closing forward alone is not sufficient but instead excessive valve overlap must also be avoided through the inventive shortening of the intake length, because otherwise an excessive amount of residual gas could have a negative effect on combustion.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.